[stgt] [PATCH 3/6] mgmt and concat_buf: using concat_buf in mgmt.c

[Alexander Nezhinsky]

>> > Can we kill rsp_buf? That is, we can simply write the response to
>> > *FILE?

>> What do you mean? To redirect the FILE* directly to the socket, somehow?

>> My implementation separated concat_buf and its use, so that it
>> is employed for response in tgtd and for request in tgtadm.
>> It leaves the resulting string in the user-supplied buffer pointer,
>> and the buffer can be handled and used as required by a specific
>> user context. Do you see anything wrong with this approach?

> I thought about more cleanup like adding something like FILE *rsp_fp.
> Then "show" functions like tgt_target_show_all just call
> fprintf. tgtd reads fp and write the data to ipc socket. I don't think
> "show" functions need to handle buffers directly.

mtask->resp_buf and mtask->resp_bsize are just holders. 
We will need some holders anyway, as the file will be opened under 
OP_SHOW case and the like (it is unnecessary in other cases).
open_memstream() takes the buffer and size pointer arguments, 
so they should be provided there, when the file opens. 
Moreover, they should be stored in a global context,
of which mtask is the only relevant one, as we need the values 
to write to the socket. 
So we end up with essentially the same scheme.   

For example, we declare FILE *fp in "struct mtask". It is initialized to NULL.
Then in functions like mgmt.c::*_mgmt(), under OP_SHOW case
we can call open_memstream() directly, mtask->fp gets a value and 
then in mtask_handler() , under MTASK_STATE_RSP_SEND case
we can uniformly check if mtask->fp is not NULL, to close it and send 
the resulting buffers.
The problem is that we have to  pass open_memstream() those pointers,
which will get the values only under  MTASK_STATE_RSP_SEND.

Perhaps we can make concat_buf a member of mtask and store the pointers
in concat_buf, so that the calls for OP_SHOW will be: 
concat_buf_init(&mtask->concat_buf) 
    (internally passing &mtask->concat_buf.ptr, &mtask->concat_buf.size 
      to open_memstream) and
concat_buf_finish(&mtask->concat_buf)

and under  MTASK_STATE_RSP_SEND case:
if (mtask->concat_buf.size)
   write(socket_fd, mtask->concat_buf.ptr, mtask->concat_buf.size)

Does this sound better?--
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